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Re: very long sparks

Stan and all,

I didn't do any smoothing, so there may be some dots or interaction
between the dots and pixels from the scanning process. 

You've done an excellent job of disecting and analyzing the picture!
Since the source is some type of impulse generator, there's probably no
heat-rise effect, since the discharge would be more like a single
lightning bolt, and it does exhibit the sinuous pattern typical of a
lightning-like discharge.  

The big ball of light at the far tower might be a flashover from one of
the lines to the tower. This often happens during strikes to
transmission lines. It can also happen during a strike to the top ground
wire if the grounding system is insufficient to handle the lightning
surge, and the tower potential rises to the point where insulator
strings flahover between the lines and the tower. For a spectacular
picture of this happening on a 115 kV transmission line, check out:
http://www.pti-us-dot-com/pti/consult/dist/gallery/champ/thehit.htm

I think the shot represents a very real event...

-- Bert --

Tesla List wrote:
> 
> Original Poster: Stan <sdarling-at-columbus.rr-dot-com>
> 
> Bert: Did you use descreening on your scanner when you scanned this
> photo in?  I notice some print screening in the photo....
> 
> For what I talk about below refer to:
> 
> http://users.better-dot-org/sdarling/longspark/longarc.gif - I drew on the
> original image in red and black
> http://users.better-dot-org/sdarling/longspark/longarc_inverted.gif - same
> image, just inverted to show detail
> 
> I agree that when I first looked at the photo I sort of scratched my
> head.  I agree the discharge path seems awfully circuitous.  Perhaps if
> the arc duration were long enough there could have been a rising
> heat/jacob's ladder effect?  Its general shape looks like the arc you
> get from a NST HV terminal to ground.
> If you look closely, it appears there might be a short rod sticking off
> the top of the tower.  Notice how the first fraction of the spark is
> very straight and much thinner than the rest?
> 
> Also, what the HECK is that big ball of light at the top of the left
> power line tower?  It seems too bright to be ordinary glare or
> relfection.
> 
> As for the shadows--yes they do seem odd.  I think it might be a daytime
> shot taken with infrared film.  The shot is taken from a building and
> the sun is behind the building.  I think the sky being black (a classic
> signature of infrared film) tricks your eyes into thinking it's night,
> thus making the shadowing appear very weird.  The strangest thing I see
> re shadowing is abotu 2/5 of the way from right side of the picture.
> Notice the three parallel slightly curved lines/shadows going at about
> 135 degress (to the back left of the picture)?  It seems these could be
> shadows from the power lines.  Of course, this shoots down the sun
> behind a building theory unless there are very bright artificial light
> sources.
> 
> As for determining scale, the best indicator I see is at the bottom
> right of the transmitting tower. There appears to be a one-story
> entrance/lobby to the base of the round tower.  If one figures it would
> be about 12 feet tall, then one can estimate the height of the tower
> fairly accurately.  I show about 8.5 x or 8.5 x 12 feet or almost
> exactly 100 ft.  The straight line distance from the spark start on the
> tower to where the spark goes off the photo is 2x the tower height, or
> about 200 ft.  Assuming the spark really did hit the power lines, and
> extending the fence off the edge of the photo, and assuming the lines
> run parallel to it, there is about 50 ft of spark not caught in the
> photo.  So total estimated spark length is about 250ft.  Of course this
> is assuming the spark is at a 90deg angle.  If it's more or less than
> that, the spark length is higher.
> 
> Comments welcome.
> 
> -Stan
> 
<SNIP>